1. Field of the Invention
The present disclosure relates to an organic light emitting display apparatus and method for manufacturing the same, and more particularly, to an organic light emitting display apparatus and method for manufacturing the same that is capable of reducing visually recognizable bubbles in the encapsulation structure.
2. Discussion of the Related Art
Currently, a liquid crystal display (LCD) apparatus is used most widely among various flat panel display apparatuses. Since the LCD apparatus is a non-emissive apparatus that does not generate light by itself, the LCD apparatus is relatively vulnerable in view of brightness, contrast ratio and viewing angle.
As a flat panel display apparatus that may solve such drawbacks of the LCD apparatus, an organic light emitting display (OLED) apparatus has received attention. Since the OLED apparatus is an emissive apparatus that generates light by itself, the OLED apparatus has brightness, contrast ratio and viewing angle that are better than those of the non-emissive apparatus. Also, since the OLED apparatus does not require a separate backlight, the OLED apparatus may be more lightweight and thinner than the LCD apparatus, and may consume less power than the LCD apparatus.
The OLED apparatus typically includes a thin film transistor, a first electrode electrically connected with the thin film transistor, a light-emissive organic layer on the first electrode, and a second electrode on the light-emissive organic layer.
Since the light-emissive organic layer is vulnerable to water and oxygen, an encapsulation structure is typically provided to prevent a light-emissive defect caused by permeation of water and oxygen into the light-emissive organic layer.
FIGS. 1 and 2 briefly illustrate cross-sectional views of OLED apparatuses having different encapsulation structures (hereinafter, referred to as “first and second type encapsulation structures”).
As illustrated in FIGS. 1 and 2, these OLED apparatuses are substantially identical to each other in that they include a TFT substrate 10, which includes a thin film transistor (not shown), and an organic light emitting element 20 on the TFT substrate 10. The organic light emitting element 20 includes a first electrode 21 on the TFT substrate 10, which is electrically connected with the thin film transistor, a bank layer 22 formed on the TFT substrate 10 on which the first electrode 21 is formed and having a bank hole for exposing at least a part of the first electrode 21 corresponding to a light emitting area, a light-emissive organic layer 23 on the part of the first electrode 21, which is exposed through the bank hole of the bank layer 22, and a second electrode 24 on the light-emissive organic layer 23.
However, as illustrated in FIG. 1, the first type encapsulation structure includes an encapsulation glass 31 spaced apart from the organic light emitting element 20 at a predetermined distance, and a frit layer 32 disposed between the TFT substrate 10 and the encapsulation glass 31 at corners of the OLED apparatus.
In the first type encapsulation structure, the encapsulation glass 31 mainly prevents oxygen/water from being permeated into the light-emissive organic layer 23 through a face of the OLED apparatus, and the frit layer 32 mainly prevents oxygen/water from being permeated into the light-emissive organic layer 23 through a side of the organic light emitting display apparatus.
However, the OLED apparatus having the first type encapsulation structure has a problem in that the OLED apparatus is vulnerable to external impact, and thus may not be suitable for a flexible display apparatus.
In order to address such a problem of the first type encapsulation structure, the second type encapsulation structure has been suggested.
According to the second type encapsulation structure, as illustrated in FIG. 2, a passivation layer 40 is formed on the TFT substrate 10, in which the organic light emitting element 20 is formed, to fully cover the organic light emitting device 20. Subsequently, an encapsulation film 60 is bonded onto the TFT substrate 10, on which the passivation layer 40 is formed, using an adhesive layer 50.
In the second type encapsulation structure, the encapsulation film 60, the adhesive layer 50 and the passivation layer 40 mainly prevent oxygen/water from being permeated into the light-emissive organic layer 23 through the face of the organic light emitting display apparatus, and the adhesive layer 50 and the passivation layer 40 mainly prevent oxygen/water from being permeated into the light-emissive organic layer 23 through the side of the organic light emitting display apparatus.
However, the conventional adhesive layer 50 applied to the second type encapsulation structure has relatively low heat-resistance. Due to such low heat-resistance and difference in coefficient of thermal expansion with an adjacent structure, the adhesive layer 50 may be thermally deformed under an environment of high temperature and high humidity, as illustrated in FIG. 3. This may lead to a problem in that fine bubbles 51 inside the adhesive layer 50 are combined with one another to generate bubble(s) 52 that may be recognized visually.
These bubbles may be regarded as a product defect, and thus the productivity of the OLED apparatus may be lowered. The occurrence of these bubbles after the product has been sold may lower reliability and damage the brand image.